Direct synthesis of isoalkanes through Fischer-Tropsch reaction on hybrid catalysts

Abstract

Sulfated zirconia combined with a Fischer-Tropsch synthesis (FTS) catalyst (RuNaY) was used to produce branched alkanes from synthesis gas. Under the reaction conditions used in this work, sulfated zirconia did not contribute to carbon monoxide conversion but brought about significant changes in hydrocarbon distribution. With increasing amounts of sulfated zirconia, the yield of C 3 hydrocarbons decreased while that of C 4 increased; changes in the yields of C 1, C 2, C 5 and C 6 hydrocarbons were negligible; more isoalkanes and less alkenes were formed. All these changes were attributed to secondary reactions of primary FTS products over the strongly acidic sulfated zirconia. These secondary reactions involved oligomerization-cracking, skeletal isomerization, hydrogen transfer and coking. Calcination temperature of sulfated zirconia had a strong effect on its activity for the secondary reactions. Coke deposition on sulfated zirconia was identified to be the main reason of the catalyst deactivation. The very strong Lewis acid sites are proposed to be responsible for the rapid coking deactivation. Addition of small amounts of platinum on SO 2− 4/ZrO 2 or mixing SO 2− 4 /ZrO 2 with the FTS catalyst instead of using them in separate layers improved the overall stability of the hybrid catalyst.